The term "catheter" is applied to any tubular instrument which is inserted into a body cavity, either naturally or surgically created, for the purpose of transporting solids, liquids and gases to or from such cavity in a controlled manner within the channel described by the tube. Catheters, capable of transporting oxygen, blood, body wastes, drugs, nutrients and other matter, are indispensible to the medical field and the art of saving lives.
The concept of the medical catheter has existed for over five thousand years. Original catheters were crudely constructed tubes made of metal Such instruments were discovered amidst the ruins of Pompeii, which was buried in the year 79 A.D. An interesting account of this early use of the medical catheter may be found in an article by Roy A. Tucker, entitiled "History and Sizing of Genitourinary Instruments," in the September 1982 issue of Urology (pages 342-349).
The origination of the modern catheter is attributed to Lorenz Heister, who developed an instrument shaped to fit the prostatic urethera in the early 1700's. Benjamin Franklin was one of the first to improve upon this idea, creating a uretheral catheter for use by a family member suffering from prostatic obstruction.
To date, the most significant development in this field has been the Foley catheter, invented by Dr. Frederick Foley around 1945. This type of catheter, would continues to be popular in the urological market despite its many problems, is inserted into the uretheral tube with the ocassional aid of a stylet: a thin metal rod placed within the catheter tube which provides some rigidity to the tube to facilitate insertion. The Foley catheter also includes a balloon at its distal end which is inflated once within the bladder to secure the tube in its desired position.
Other catheters, although not as well known as the Foley catheter, provide certain advantages for specific applications. Some of these catheters are improvements upon the Foley catheter while others provide completely innovative solutions to specific application problems.
Schiff U.S. Pat. No. 4,467,790 discloses an intra-aortic catheter which posesses a balloon which is capable of being elongated and therefore reduced in its diameter so that it may fit through a small diameter percutaneous sheath inserted into an artery.
Fuqua U.S. Pat. No. 4,601,713 discloses a variable diameter catheter which may be folded longitudinally to facilitate insertion, reducing the risk of infection and minimizing trauma.
Lin U.S. Pat. No. 4,211,233 discloses a balloon catheter with provisions to facilitate insertion and removal by means of releasing lubricants from openings in the side of the catheter.
Taylor U.S. Pat. No. 4,259,960 discloses an arrangement which is intended to prevent the balloon segment of a catheter from adhering to the shaft of a catheter.
Chin and Fogarty U.S. Pat. No. 4,493,711 discloses a cartheter posessing a partially-folded section at its distal end, which is activated by means of pressurized non-compressible fluid.
This last reference is one of two prior art patents believed to have any relevance to the present disclosure. This is due to the characteristic action at the distal end of that tube. However, the tip of that catheter is an "inverted-evertable non-elastic" section which is a piece separable from the tube, made of a material different from the material of the tube, and of "a diameter throughout equal to or greater than the catheter body." Furthermore, that catheter assembly requires multiple folds at the end of the "inverted-evertable" section to seal the tip during its extension to a predetermined length. This "multi-fold" configuration proves detrimental to the intended purpose of the tube due to the abrasion which occurs as the folded sections unfold. Subsequently, that catheter must be forcibly moved into and out of the body in the same manner as any conventional catheter, with its walls moving abrasively relative to the body tissue it comes into contact with. Also, that catheter posesses no provisions for retraction of the evertable section, does not allow for fine control of the length of the everted section, does not provide for precise control of the speed of extension, does not indicate to the physician the exact position of the distal end and requires a valve and piston arrangement and a non-compressible "pressurized fluid" for deployment of the inverted section, which remains completely closed until that catheter is fully extended.
The other prior art patent which should be noted is Cunningham U.S. Pat. No. 4,318,404, which provides "an applicator for a member having a surface," such as a tampon. This applicator works by allowing the surface of the member to be "exposed by relative movement of one of the walls of the applicator with respect to the member." This applicator is not hollow, does not provide for the transfer of fluid, is not doubled along its entire length within the channel, does not remain doubled throughout its operation, must be removed from the channel in an abrasive manner, employs a push-stick arrangement for control, is not intended to be secured or otherwise locked in place, does not indicate to the operator either the position of the end of the tube or the position of the member and the foldout surface provides significant benefit only to the member being exposed and not to the body channel in which it is inserted, since resistance and irritation are produced by both the surface of the member moving against the walls of the body channel as it becomes exposed, as well as resistance caused by the insertion and removal of the applicator. Additionally, it is not intended to be retracted or otherwise controlled and claims a "flexible applicator" and "thin polyresin sleeve" made of a "non-absorbant material".
Other patents which provide a further understanding of the present state of the art and the practical problems and uses of catheters are: Fogarty et al. U.S. Pat. No. 4,271,839, Sheridan U.S. Pat. No. 4,109,659, Kramann et al. U.S. Pat. No. 4,043,345, Silverman U.S Pat. No. 3,168,092, and Fisher U.S. Pat. No. 4,211,234.
The variety of uses for medical catheters, including specific requirements for each type of application, creates many opportunities for new catheter development. This is apparent in the list of related patents presented previously, as each invention attempts to overcome one or two significant problems with its predecessors. In most instances, these solutions are created at the cost of some new complication.
The value of any catheter is directly related to the specific advantages and disadvantages posessed by its design, in combination with the priority of needs of the application for which it is intended. Therefore, in order to assess the potential for any new catheter development, it is necessary to be aware of the most significant problems associated with catheter use today:
Sterility: Maintaining sterility of a conventional catheter, once removed from its sterile package environment, poses many problems. The exterior surface, which will be in contact with body tissue, must be handled and is often exposed to non-sterile surfaces, especially when employed in emergency and field operations.
Insertion: The introduction of a conventional catheter into an opening may prove difficult, due to the size of the opening, lack of definition of the opening and catheter-handling complexities. Proper insertion proves to be a virtually impossible feat at times when the patient is not stationary or cooperative.
Restricted Entry: In certain instances, it is necessary to insert a catheter into a forcibly closed opening or through a channel constriction. This usually requires a special instrument to either pry open the passage, or the use of a guide wire enclosed within the catheter to stiffen the tube so that it may be forced through.
Speed of Use: The need for special handling to ensure sterility, the use of instruments to facilitate insertion, lubricants, and the like, restrict the speed with which a conventional catheter may be employed. This places patients at greater risk, while consuming the otherwise useful time of medical personnel.
Lubricants: Applications of a lubricant to the surface of a conventional catheter prior to introduction, or to the entrance of the channel, in order to facilitate insertion are extremely common. These lubricants are often pushed ahead of the tip of the catheter or wiped off as the catheter enters the channel.
Tissue Trauma: As a result of the need for force in many catheter introduction situations, tissue at the opening and tissue at any point along the channel may be traumatized. This may include irritation, further constriction of the channel, and hemorrhaging.
Infection: Control of bacteria is the most serious problem arising from catheter use today. Conventional catheters tend to drag bacteria and other debris along the surface of the channel as the tube is being pushed in or pulled out. This produces a risk of infection as the tube is inserted, due to likely exposure of the surface of a conventional catheter to an unsterile environment. This movement of a conventional catheter also increases the likelihood of bacteria spreading along the length of the channel.
Direct Placement: Due to the stresses which are caused by the surface of a conventional catheter against adjacent body tissue as it is moved into and out of a channel, conventional catheters are placed so that they lead from the body cavity being served to the exterior surface of the body in as direct a route as possible. This often complicates surgical procedures, placing patients at greater risk.
Channel Obstruction: Conventional catheters often cause great difficulty when they encounter an obstruction while being pushed through a channel. This requires twisting and pushing the tube, or occasionally compromising or abandoning a procedure.
In-channel Situation Analysis: Conventional catheters are incapable of providing the physician with any accurate method of determining the situation within a channel.
Tube Security: Most catheter products on the market today employ a complicated ballon structure which inflates to prevent the distal end of the tube from being pulled out of a cavity, or which inflates within a channel to create resistance against the walls of the channel, thereby preventing undesirable movement. This balloon structure requires a means for controlling inflation and is prone to imperfect operation.
Repositioning: Once a catheter is positioned, it is often desirable to make adjustments in the placement of the tube. Conventional catheters pose all the previously noted movement problems, further complicated by a deterioration in lubricant effectiveness within a short period of time.
Removal: As a conventional catheter is pulled from a channel, shear stresses are created in adjacent body tissue. Additionally, when a flexible conventional catheter is pulled out along a non-linear path, force components transverse to the tube are created, acting to displace body tissue in the vicinity of these bends and further increasing shear stress. The consequences of these forces may include irritation, tissue trauma, further channel constriction and painful, difficult removal of a conventional catheter.
Residual Irrigation: Since many types of conventional catheters must be introduced partialy into a cavity to allow for inflation of a balloon, the drainage function may be impaired. Furthermore, a balloon may actually force matter into the peri-catheter space between the tissue of the channel and the exterior surface of the tube, similar to a plunger.
Pain to the Patient: The ultimate goal of any medical procedure involves the well-being of the patient. Therefore, control of discomfort and pain during the placement, repositioning, continued use and removal of a catheter is most important. Conventional catheters do little to prevent or minimize patient discomfort. In addition to the emotional suffering by a patient, pain and discomfort often place a patient at greater risk, due to conscious resistance to a procedure and continued psychological effect.
Cost Effectiveness: The complexity of many catheters, including design variations which serve only to overcome basic problems, leads to a high initial cost. This is relatively insignificant, however, when compared to the cost associated with subsequent catheter-related complications, which may easily be hundreds or thousands of times the initial price of even the most expensive catheter. Only a catheter which minimizes these subsequent expenses, as well as being reasonably priced, may be considered completely cost effective.
Any catheter which could overcome these problems posses the potential of saving lives. Although this may be considered the primary intent of the invention disclosed by this patent, the significance of commercial value, as measured by the presence of market demand, is recognized as the factor which will ultimately determine the real value of any new product.
One example of the existance of such demand, exposing the immediate need for a new development in the urological catheter segment of the market, is the widespread use of Foley-type tubes. The Foley catheter is one of the most successful medical products in history, selling more units than any other tray or kit on the market today (Frost and Sullivan Report #A1139, Prepackaged Kits and Trays--Markets in the U.S., .COPYRGT.1983). Yet, this is despite some very major problems directly related to its use, such as catheter-induced infection, troubled insertion, and leakage. A study appearing in the New England Journal of Medicine and recounted in the Frost & Sullivan Report noted above suggests that over 56,000 deaths per year may be directly attributed to the use of Foley-type tubes in the United States alone. This unacceptable figure becomes even more staggering when other catheter applications and their related consequences are accounted for worldwide. A multiple-use catheter product line, which overcomes most of the present difficulties relating to catheter use, would present a vast opportunity.